1. Field of the Invention
The present invention relates to an antenna system and an antenna thereof. More particularly, the present invention relates to an antenna system comprising a plurality of antennas, and the antenna thereof, wherein each of the antennas has a slot area with a Y-shaped or T-shaped geometric profile.
2. Descriptions of the Related Art
Radio frequency identification (RFID), one solution of automatic identification technologies, relies on radio frequency (RF) electromagnetic waves to communicate between an RFID tag and a transmitter or a reader. In some applications, the transmitter and the reader are combined into a single device. An RFID tag is a small object attached to or implanted in an article, an animal's or a person's body for identification purpose, and carries information of the article, the animal or the person. To obtain such information, a reader should be installed at a nearby location to receive RF electromagnetic waves transmitted from the RFID tag so as to retrieve information corresponding to the article, the animal or the person from the RF electromagnetic waves. Some technologies currently available may support the communication between the RFID tag and reader or a transmitter several meters away from each other. The RFID is used in a variety of applications which requires the wireless identification or recording for articles. One of these applications is the checkout system in a supermarket.
There are two categories for RFID systems in terms of reading distance. One is the near-field RFID that reads the information by using magnetic field induction within a distance of centimeters. The other one is the far-field RFID that reads the information by using electric field induction within a distance ranging from several to tens of meters. For the checkout system, sensing RFID tags and reading information need to be performed non-directionally in a limited space. Hence, a near-field RFID is generally adopted in the checkout system.
As shown in FIG. 1, an antenna 1 used in a near-field RFID to detect RFID tags comprises a metal area 11 and a slot area 13. The metal area 11 is coated by a metal material. The slot area 13 allows electromagnetic waves to pass through and generate a magnetic field to detect the RFID tag. Dimensions of the slot area 13 are associated with an operating frequency band of the RFID system. More specifically, with adjusting the dimensions of the slot area 13, the antenna 1 will operate at different frequency bands ranging from 880 MHz to 960 MHz. Due to the geometric profile of the slot area 13 shown in FIG. 1, the magnetic field generated by electromagnetic waves passing through the slot area 13 only can detect the RFID tag in a single direction. For example, when an article passes through the antenna 1 along the Y axis direction, the antenna 1 is able to detect the RFID tag attached thereon and successfully read the information. However, if the article passes through the antenna 1 along the X axis direction instead, the antenna 1 fails to detect the RFID tag. Consequently, the information in the RFID tag cannot be read. Therefore, many inconveniences may exist when using the antenna 1 shown in FIG. 1 to detect RFID tags. Furthermore, if the antenna 1 in FIG. 1 is used for detecting RFID tags in a supermarket, customers have to line up all goods with RFID tags thereon facing the same direction when checking out. Otherwise, checkout errors will occur if any RFID tag is not detected.
In view of this, it is highly desirable in the art to design an antenna system capable of reading an RFID tag in any directions.